• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.331-339
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• 2019

While high-temperature ceramic composites consisting of carbides, borides, and nitrides, the so-called ultra-high-temperature ceramics (UHTCs), have been commonly produced through solid-state sintering, melt-solidification is an alternative method for their manufacture. As many UHTCs are binary or ternary eutectic systems, they can be melted and solidified at a relatively low temperature via a eutectic reaction. The microstructure of the eutectic composites is typically rod-like or lamellar, as determined by the volume fraction of the second phase. Directional solidification can help fabricate more sophisticated UHTCs with highly aligned textures. This review describes the fabrication of UHTCs through the eutectic reaction and explains their mechanical properties. The use of melt-solidification has been limited to small specimens; however, the recently developed laser technology can melt large-sized UHTCs, suggesting their potential for practical applications. An example of laser melt-solidification of a eutectic ceramic composite is demonstrated.

• Journal of Korea Foundry Society
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• v.15 no.3
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• pp.262-271
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• 1995

It is well known what is impossible to refine primary and eutectic Si simultaneously by addition of both Cu-P and Sr(or Na). Because of the formation of compound $Sr_3P_2(or Na_3P)$ in the melt, in the result, both effects disappear. In this study Al-Cu-P alloy that comprises AlP compounds inside is added in the melt with Sr simultaneously. As AlP compounds that act on nucleation sites of primary Si are not formed but added directly an the melt, it is difficult to form $Sr_3P_2$ by reaction with Sr. Therefore it is possible to refine primary and eutectic Si simultaneously in the general casting process by use of Al-Cu-P alloy and Sr.

• Journal of Korea Foundry Society
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• v.32 no.6
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• pp.261-268
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• 2012

The effects of thickness, base element and additive to inoculant on the number of eutectic cells and chill depth of thin-section gray cast iron were investigated. Meanwhile the number of eutectic cells increased by inoculation, chill depth decreased. The former decreased and the latter increased by holding the melt at the temperature range between 1,450 and $1,500^{\circ}C$. The former was more for the thinner casting with the thickness of 5 mm than the other. The result of thermal analysis coincided well with the change of macrostructure. The former increased and the latter decreased with the increased contents of carbon, silicon and the silicon content by inoculation. The former decreased and the latter increased with increased manganese content. The number of eutectic cells decreased as the amounts of rare earth and the bismuth added to this inoculant increased. With the addition of sulfur of 0.10 wt% of the weight of this inoculant, the maximum number of eutectic cells was obtained.

• Journal of Korea Foundry Society
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• v.29 no.2
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• pp.78-85
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• 2009

Functionally graded microstructure of centrifugal cast Al-Si alloy, especially distribution of primary Si particles according to the changes of melt pouring temperature and rotation frequency was investigated by numerical simulation. Moving velocity of Si particles increased as the melt pouring temperature and rotational frequency of mold increased. Therefore, segregation tendency of primary Si particles toward inner side of cylindrical sample increased as the melt pouring temperature and rotational frequency of mold increased. Rich distribution region of particles was located at 0.9, 0.7, 0.4 mm from inner surface of cylindrical sample under the centrifugal cast condition of $750^{\circ}C$ melt pouring temperature and 1500, 2000 and 2500 rpm mold rotational frequencies, respectively, by numerical simulation.

• Journal of Korea Foundry Society
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• v.36 no.2
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• pp.53-59
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• 2016

The effects of ultrasonic melt treatment on the microstructures of aluminum piston were examined at five observation parts having different cooling rates. The microstructure of aluminum piston consisted of primary Si, eutectic Si, and various types of intermetallic compounds. Regardless of cooling rate, the ultrasonic melt treatment transformed dendritic eutectic cells to equiaxed eutectic cells and it decreased the sizes of eutectic Si and intermetallic compounds that exist at eutectic cell boundaries. In the absence of ultrasonic treatment, coarse primary Si particles were severely segregated and its size was increased with decreasing the cooling rate. The ultrasonic treatment decreased the size of primary Si particles from $25.5{\sim}31.0{\mu}m$ to $17.6{\sim}23.1{\mu}m$, depending on the cooling rate. In the presence of ultrasonic treatment, relatively fine primary Si particles were homogeneously distributed throughout the piston. In addition, the ultrasonic treatment increased the population density and area fraction of fine primary Si particles.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2041-2046
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• 2004

Recently series of steam explosion experiments have been performed in the TROI facility to identify the influence of corium compositions on the occurrence of a spontaneous steam explosion varying corium melt composition. The compositions of the corium were 0 : 100, 50 : 50, 70 : 30, 80 : 20 and 87 : 13 at weight percent of $UO_2$ to $ZrO_2$, and the mass of the corium was about 10kg. Corium melt at 0 : 100 weight percent (pure zirconia) caused a strong spontaneous steam explosion, and melt at 70 : 30 weight percent(eutectic corium) led to a weak steam spike, while melts at other compositions did not result in spontaneous steam explosions, when they came into contact with 67cm deep water pool at room temperature. It seems that the explosivity of pure zirconia is stronger than that of corium at other compositions and a steam explosion is not likely to occur with corium melts at non-eutectic compositions which are included in mushy zone region.

• Journal of Korea Foundry Society
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• v.29 no.2
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• pp.64-69
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• 2009

In the present study the effect of cooling rate during solidification on the microstructural characteristics of Al-xAg (x = 31, 33, 35 at.%) in-situ binary eutectic composites has been investigated. To provide a wide range of cooling rate three different casting techniques, i.e. conventional casting, injection casting, and melt spinning have been used. The observed microstructure is very much dependent on the cooling rate. The fcc ${\alpha}$-Al and hcp $Ag_2Al$ phases exhibits an orientation of (111)Al//(0001)$Ag_2Al$, [1-10]Al//[11- 20]$Ag_2Al$. The microstructure of the melt-spun samples contains Widmanstatten structure resulting from solid-state transformation and nano scale two-phase structure resulting from solid-state phase separation. The microstructure of injection-cast samples contains eutectic structure and solid state phase-separated structure. On the other hand, conventional-cast samples exhibit a microstructure consisted of plate-type eutectic structure.

• Journal of Korea Foundry Society
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• v.31 no.3
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• pp.137-144
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• 2011

The effects of thickness, base element and inoculants on the number of eutectic cells and chill depth of gray cast iron plate casting were investigated. Meanwhile the number of eutectic cells increased by inoculation, chill depth decreased. The former decreased and the latter increased by holding the melt at the temperature range between 1,450 and $1,500^{\circ}C$. The former was more for the thinner casting with the thickness of 5 mm than the other. The result of thermal analysis coincided well with the change of macrostructure. The former increased and the latter decreased with the increased contents of carbon, silicon and the silicon content by inoculation. The former decreased and the latter increased with increased manganese content. The performance of the Superseed Extra was the best among 5 inoculants.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.1
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• pp.41-48
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• 2010

Uranium deposits from an electrorefining process contain about 30% salt. In order to recover pure uranium and transform it into an ingot, the salts have to be removed from the uranium deposits. Major process variables for the salt distillation process of the uranium deposits are hold temperature and vacuum pressure. Effects of the variables on the salt removal efficiency were studied in the previous study[1]. By applying the Hertz-Langmuir relation to the salt evaporation of the uranium deposits, the evaporation coefficients were obtained at the various conditions. The operational conditions for achieving above 99% salt removal were deduced. The salt distilled uranium deposits tend to form the eutectic melt with iron, nickel, chromium for structural material of salt evaporator. In this study, we investigated the hold temperature limitation in order to prevent the formation of the eutetic melt between urnaium and other metals. The reactions between the uranium metal and stainless steel were tested at various conditions. And for enhancing the evaporation rate of the salt and the efficient recovery of the distilled salt, the thermal analysis of the salt distiller was conducted by using commercial CFX software. From the thermal analysis, the effect of Ar gas flow on the evaporation of the salt was studied.

• Bulletin of the Korean Chemical Society
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• v.29 no.1
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• pp.127-129
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• 2008

EPR spectroscopic technique was applied for a quantitative analysis of Eu(II) for a speciation of europium in a LiCl-KCl eutectic melt. By adopting the first absorption line of each isotopes (151Eu and 153Eu), a calibration plot was obtained. The calibration of the EPR intensity shows a good linearity according to the amount of Eu(II). The EPR intensity was identified to increase proportionally with a decrease of the attenuation parameter for EPR microwave power. The fluorescence technique was used qualitatively to find whether either of Eu(II) or Eu(III) ions exists in a molten salt sample. The ICP-AES technique was also adopted to determine the total concentration of europium in the sample, since EPR is only sensitive for detecting the Eu(II) ion. The extent of the reduction of Eu(III) in the LiCl-KCl eutectic melt at 723 K was determined by using this technique.